Your first str.format() call is a regular method call with 3 arguments, there is no tuple involved there. Your second call uses the * splat call syntax; the str.format() call receives 3 separate individual arguments, it doesn't care that those came from a tuple.

Formatting strings with f don't use a method call, so you can't use either technique. Each slot in a f'..' formatting string is instead executed as a regular Python expression.

You'll have to extract your values from the tuple directly:

f'{t[0]}, {t[1]}, {t[2]}'

or first expand your tuple into new local variables:

a, b, c = t
f'{a}, {b}, {c}'

or simply continue to use str.format(). You don't have to use an f'..' formatting string, this is a new, additional feature to the language, not a replacement for str.format().